Experiments will continue to analyze the electrical behavior of the plasma membrane of Neurospora with the objective of extracting detailed current-voltage relationships for the H ion /glucose cotransport system, the electrogenic ATP-dependent proton pump, and a newly discovered derepressible transport system for NH4 ion. From these I-V curve data, we should attempt to construct kinetic models for the operation of electrogenic pumps. In addition, experiments will be begun to analyze the ionic noise of the plasma membrane of Neurospora, in order to obtain estimates of fluxes which are independent of the usual electrophysiological assumptions. This methodology would appear to be most important for ions, such as H ion, whose unidirectional fluxes cannot be measured by isotopic means. BIBLIOGRAPHIC REFERENCES: Slayman, C.W., and C.L. Slayman, 1975. Energy coupling in the plasma membrane of Neurospora: ATP-dependent proton transport and proton-dependent sugar cotransport, in H.R. Kaback, et al., eds., "Molecular Aspects of Membrane Phenomena," Springer Verlag (Berlin) pp.233-248. Gradmann, D., and C.L. Slayman, 1975. Oscillations of an electrogenic pump in the plasma membrane of Neurospora. J. Membrane Biol. 23:181-212.